Switchable leads?

Submitted by RickG on Wed, 01/04/2012 - 12:35

Love what you're doing here!

The input jack has three tabs for two wires. One tab is the tip, does it matter which of the other tabs is selected?

What about adding a similar output jack for an external speaker cabinet?
Is there a way to set it up where the output would go directly to self-contained speaker, unless the jack was in use, in which case output would go through the jack? Should this be hard to do? Any thoughts on how?

Similarly, on the power supply, is there a way to put in automatic switching between a wall wart and the AA battery box?

Let me know what you think.

Thanks

Member for

11 years 5 months

John

Sat, 01/14/2012 - 16:15

The input jack has three tabs for two wires. One tab is the tip, does it matter which of the other tabs is selected?

The three tabs are, counting from the tip, the tip, the ring, and the sleeve. Use the sleeve for connecting to ground. If you connect the negative end of the power supply to the ring, and to the ring only, and connect all other grounds to the sleeve, then when you plug in a cable, the amp will turn on, and when you unplug, it will turn off.

What about adding a similar output jack for an external speaker cabinet?
Is there a way to set it up where the output would go directly to self-contained speaker, unless the jack was in use, in which case output would go through the jack? Should this be hard to do? Any thoughts on how?

You would use a switched output jack:

http://www.mouser.com/ProductDetail/Neutrik/NMJ6HC-S/?qs=sGAEpiMZZMvlX3…

The way this works is, there are six terminals. Ignore the middle one, you don't need it. If you are looking at the end you plug in to, the signals come in on the right, positive to the tip, negative to the sleeve. See those arched bits of metal on the right? Those are bent metal springs. If there is no jack plugged in, those springs press against the terminals on the other side of the jack. You would plug your speaker into those terminals on the left.

When you plug in a jack, the springs press down on the plug in the jack, and at the same time, they lift from the speaker terminals, cutting power to the speaker and supplying it to the jack.

Obviously this is for external speaker power only, you wouldn't want to plug in any headphones to that jack because you'd fry them (and your ears in the process). Do not supply power to the ring terminal, you might think it would be cool because you could supply power to two speakers at once but what happens if someone plugs a mono jack in your output terminal? Oh right, they just shorted the output of the amp to ground and probably fried your power chip. Oooops.

Similarly, on the power supply, is there a way to put in automatic switching between a wall wart and the AA battery box?

My first thought was something similar to how the Arduino switches between USB power and wall power:

http://forums.adafruit.com/viewtopic.php?f=25&t=12406

But I looked at that circuit diagram and it would take a bit of reworking and testing.

If you want to give up the automatic switching, for 3.48 plus shipping you can get one of these switches from Digikey:

http://search.digikey.com/us/en/products/A103SYCB04/450-1525-ND/1021735

Wire the positive battery wire to one end of the switch, positive wall voltage to the other end, and run a wire from the center lug to the +V input on the Stella amp. When the switch is in the middle, it's off, when it's to either side, it's taking power from the appropriate source. For another buck you can get the same switch with solder lugs so it's easier to solder the wires on:

http://search.digikey.com/us/en/products/A103SYZQ04/450-1527-ND/1021787

You can get one at Mouser too, it's even a buck cheaper:

http://www.mouser.com/ProductDetail/TE-Connectivity-Alcoswitch/A105SYCB…

Disclaimer: you may want to do your own research, I haven't tested any of this. But it should work.